Fix participants' profile pictures (avatars) from the last Summit

[DinisCruz]

(I believe this is caused by a recent linked in change in how they map their images)

(for example https://media.licdn.com/mpr/mpr/shrinknp_400_400/p/2/005/04a/086/1c3ff3d.jpg)

[fzipi]

I am trying to find a common path for this, because if not we will need to link all images again.